This invention relates to organic inhibitor treating solutions employed to reduce corrosion from harsh fluid environments. More particularly, the invention concerns treating solutions containing thiol esters.
Corrosion that occurs in an oil field environment is extremely complex and tends to attack all manner of metal equipment above and below ground. The principle corrosive agents found in the well fluids include hydrogen sulfide, carbon dioxide, oxygen, organic acids and solubilized salts. These agents may be present individually or in combination with each other. Valves, fittings, tubing, pumps, precipitators, pipelines, sucker rods and other producing equipment are particularly susceptible. Deposits of rust, scale, corrosion by-products, paraffin and other substances create ideal environments for concentration cells. Carbon dioxide and hydrogen sulfide induced pitting is encouraged by such deposits. Acidic condensate that collects on metal tubing will also cause pitting. Extreme temperatures and pressures in downhole environments further accelerate corrosion.
Very often as oil fields mature and enhanced recovery methods such as water flooding are instituted, the concentration of hydrogen sulfide in the well fluids increases dramatically. This increase in concentration and its related effect on the extent of pitting corrosion may make older fields economically unattractive due to to excessive corrosion costs.
Various sulfur compounds have been employed for many years in corrosion inhibitor systems, either alone or in combination with other components of inhibitor systems, such as amines, amides, surfactants, various aromatic compounds, phosphorus compounds and solubilizers. Dithiolanes having a specified formula of RR'COR" are proposed in U.S. Pat. No. 2,912,386 as corrosion inhibitors for acid attack on steel. According to the patent, R is a univalent organic radical having a specified formula, R' is a divalent hydrocarbon radical of less than 8-carbon atoms, and R" is OH, NH.sub.2, lower alkoxy or an alkali metal such as Na. The preferred additive is 5-(1,2-dithiolan-3-yl)pentanoic acid. U.S. Pat. No. 3,791,789 discloses dithiolium compounds as corrosion inhibitors. And U.S. Pat. No. 3,697,221 describes the use of thionium derivatives, especially quaternary derivatives of dithiole-3-thiones as corrosion inhibitors.
U.S. Pat. No. 2,474,603 describes the use of corrosion inhibition systems containing a mixture of a butyl mercaptan along with sulfur containing compounds such as sulfides. A discussion on the use of alkyl mercaptans is also contained in Travanelli, Zucchi, Gullini and Carssiti, "Inhibition of Acid Corrosion of Iron By Sulfur Organic Compounds", Ninth International Congress on Metallic Corrosion, p. 602-5 (1969).
An aliphatic dithiol of the formula HS(CH.sub.2).sub.n X(CH.sub.2).sub.m SH where X equals O, S or NH, and n and m equals 1-20, is disclosed in Chemical Abstracts 88: 40725p. A lubricating oil additive with excellent antioxidant anticorrosion properties is disclosed in U.S. Pat. No. 4,188,297. This lubricating additive is the reaction product of olefins with sulfur and certain mercaptans wherein the reaction product contains a high percentage of sulfur, such as about 25% sulfur. U.S. Pat. No. 4,495,336 discloses the use of mercapto-polycarboxylic acids as corrosion inhibitors.
Other examples of sulfur containing corrosion inhibitors include thiophosphates disclosed in U.S. Pat. No. 3,984,203 and various combinations of amido, and mercapto or polymercapto groups described in U.S. Pat. No. 4,332,967. U.S. Pat. No. 4,350,600 discloses a corrosion inhibitor for high temperature and high pressure gas wells containing a dialkyl disulfide along with a relatively high molecular weight aliphatic amine.